This invention relates to bearings. In particular, this invention relates to a polymeric bearing system for a rotating shaft, and a bearing surrounded by a bonded elastomer sleeve, and fractional horsepower motors containing same.
Polymeric bearings have been used for years in many applications where the working conditions require oscillating, reciprocating, or continuous motion, such as small electrical motors. In a conventional motor, the rotor shaft extends through a housing formed from brackets that cover each end of the rotor opening, and are secured to the stator. The housing restrains the rotor shaft, and thus the rotor body, against substantial axial displacement relative to the stator, and supports bearings in which the shaft rotates. The bearings maintain stability and alignment of the rotor while allowing for substantially free rotation of the rotor shaft.
Such electrical motors are particularly needed for applications in which the motor runs for extended intervals over prolonged periods of time, which may be many years. As such, the motor must be extremely durable, highly resistant to failure and preferably requiring little maintenance over its useful life. The components which tend to be most problematic in achieving these parameters are the bearings because they are subject to persistent frictional contact with the rotating shaft over the life of the motor.
Several types of bearing systems are available. An electrical xe2x80x9cdryxe2x80x9d motor generally consists of a rotor with wound electrical wire fuming in a housing, called a stator, where magnets are installed circumferencially. The shaft of the rotor has to be supported by at least two bearings that function to keep the rotor well centered in the stator and provide a smooth rotation with minimal friction loss. As there is no perfect alignment, and if the motor has to turn both clockwise and counterclockwise, an axial force along the shaft is created by the system. The load then has to be carried by either a thrust washer or through the use of a ball bearing.
Polymeric plane bearings working in dry motors are known to produce much noise and vibrations that cause wear of the bearings, a significant decrease of the motor""s rotational speed, and reduced motor life.
It is also known to press fit journal bearings tightly to a bearing bracket. This type of bearing may require machining after the press fitting operation, which significantly increases the manufacturing cost of the motor. Although a press fit journal bearing will remain in place in the bearing bracket during assembly, due to the interference fit between the bearing and the housing, the performance of the motor at times may be less than optimum because the fixed position of the bearing does not allow for even slight deviations in rotor shaft alignment. If the motor is jarred or bumped during operation, severe noise and vibration can result.
Also known are shaded pole type motors which typically utilize spherical diameter, oil impregnated powdered metal bearings or ball bearings held in place by die cast aluminum or zinc bearing brackets. These types of bearings require constant exposure to a lubricant. In a hydrodynamic system, the motor shaft is supported by an oil film, and it has been found that this oil film causes instability of the system. This hydrodynamic lubrication system is not applicable to the present invention since the nature of the instability phenomenon is different than that of the dry motor system to which the present invention is directed.
A continuing need has existed for a dry motor bearing system that solves the problem of noise and vibration thus allowing stable continuous rotation of the bearing, increasing motor stability and reliability and prolonging motor life.
The present invention relates to a composite bearing system where a polymeric material with good self-lubricating properties is surrounded by an elastomer sleeve having good dampening characteristics, thereby enabling the capability of dry continuous rotation of the bearing with reduced noise and vibration, thus reducing wear on the bearing and extending the life of the bearing system and of the motor.
The invention also provides a fractional horsepower motor, comprising a rotor rotationally disposed in a stator, stator windings disposed about the stator for driving the rotor and a rotating shaft rotationally fixed to the rotor, and a bearing system comprising a bearing connectedly surrounded by an elastomer sleeve to reduce noise and vibration of the bearing system thereby increasing motor stability and reliability and prolonging motor life.
In a still further aspect of the invention, the bearing system comprises a bearing retainer for ease of assembly of the bearing system into a housing of the motor.